Pre-reformer

ABSTRACT

A pre-reformer ( 10 ) comprises a non-electrically conducting gas tight duct ( 12 ) and an electrically conducting wire ( 14 ) arranged in the duct ( 12 ). The electrically conducting wire ( 14 ) is electrically isolated from the duct ( 12 ). The duct ( 12 ) has an inlet ( 16 ) for receiving a hydrocarbon fuel at a first end ( 18 ) and an outlet ( 20 ) for supplying a pre-reformed hydrocarbon fuel at a second end ( 22 ). At least the inner surface ( 24 ) of the duct ( 12 ) is chemically inert with respect to the hydrocarbon fuel. An electrical power supply ( 26 ) is electrically connected to the electrically conducting wire ( 14 ) and a control means ( 28 ) controls the supply of electrical current through the electrically conducting wire ( 14 ) to maintain the electrically conducting wire ( 14 ) at a temperature to provide selective thermal decomposition of higher hydrocarbons in the hydrocarbon fuel. The performer reduces coking in associated fuel cells and other parts of a fuel cell system.

The present invention relates to a pre-reformer, in particular to apre-reformer for fuel cells and more particularly to a pre-reformer forsolid oxide fuel cells.

Conventionally a fuel cell system comprises a fuel cell stack and anexternal reformer, or an internal reformer. The fuel cell stackcomprises a plurality of fuel cells. The reformer reforms hydrocarbonfuel to a hydrogen based fuel suitable for use in the fuel cells in thefuel cell stack.

A problem associated with fuel cells operating with a reformer is thatthe higher hydrocarbons in the hydrocarbon fuel are not always reformed,or removed, in the reformer and this may subsequently lead to the higherhydrocarbons coking in the fuel cells or other parts of the fuel cellsystem.

Conventional ways of removing the higher hydrocarbons from thehydrocarbon fuel are complex and require additional reactant streams andare subject to the pressure and the temperature constraints of the fuelcell system.

Accordingly the present invention seeks to provide a novel reformer,which reduces, preferably overcomes, the above-mentioned problem.

Accordingly the present invention provides a pre-reformer comprising agas tight duct and at least one electrically conducting member arrangedin the duct, the at least one electrically conducting member iselectrically isolated from the duct, the duct has an inlet for receivinga hydrocarbon fuel at a first end and an outlet for supplying apre-reformed hydrocarbon fuel at a second end, at least the innersurface of the duct is chemically inert with respect to the hydrocarbonfuel, an electrical power supply electrically connected to the at leastone electrically conducting member and control means to control thesupply of electrical current through the at least one electricallyconducting member to maintain the at least one electrically conductingmember at a temperature to provide selective thermal decomposition ofhigher hydrocarbons in the hydrocarbon fuel.

Preferably the gas tight duct is non-electrically conducting.

Preferably the gas tight duct comprises a ceramic, a glass-ceramic or aglass.

Preferably a temperature sensor is arranged to measure the temperaturein the duct and is electrically connected to the control means.

Preferably the at least one electrically conducting member extendsthrough the walls of the duct and is directly electrically connected tothe electrical power supply.

Preferably the electrically conducting member is electrically isolatedfrom the duct by glass seals or glass-ceramic seals.

Alternatively the at least one electrically conducting member forms aloop, a second electrically conducting member is arranged outside theduct, the second electrically conducting member is electricallyconnected to the electrical power supply and the control means controlsthe supply of electrical current through the second electricallyconducting member to maintain the at least one electrically conductingmember at a temperature to provide selective thermal decomposition ofhigher hydrocarbons in the hydrocarbon fuel.

The at least one electrically conducting member may comprise ahoneycomb.

Alternatively the at least one electrically conducting member comprisesat least a portion of the duct.

Preferably the at least one electrically conducting member comprises ametal or an alloy.

Preferably the outlet of the duct is connected to a fuel cell stack.

Preferably the outlet of the duct is connected to a solid oxide fuelcell stack.

Preferably the outlet of the duct is connected to the fuel cell stackvia means to remove particulate carbon from the pre-reformed hydrocarbonfuel.

Preferably the means to remove particulate carbon comprises an inertialseparator. The inertial separator may comprise a twister.

Alternatively the means to remove particulate carbon comprises a filteror an electrostatic separator.

Preferably the means to remove particulate carbon from the pre-reformedfuel is connected to the fuel cell stack via a reformer.

The present invention will be more fully described by way of examplewith reference to the accompanying drawings in which:

FIG. 1 is a longitudinal cross-sectional view through a pre-reformeraccording to the present invention.

A pre-reformer 10, as shown in FIG. 1, comprises a non-electricallyconducting gas tight duct 12 and an electrically conducting wire 14arranged in the duct 12. The electrically conducting wire 14 iselectrically isolated from the duct 12, for example by glass seals 30and 32. The duct 14 has an inlet 16 for receiving a hydrocarbon fuel,for example natural gas, at a first end 18 of the duct 12 and an outlet20 for supplying a pre-reformed hydrocarbon fuel, for example methane,at a second end 22 of the duct 12. At least the inner surface 24 of theduct 12 is chemically inert with respect to the hydrocarbon fuel andpreferably the duct 12 comprises a ceramic material, a glass-ceramicmaterial or a glass material. An electrical power supply 26, eitherdirect current or alternating current, is electrically connected to theelectrically conducting wire 14, a control means 28 is arranged tocontrol the supply of electrical current from the electrical powersupply 26 and a temperature sensor 33 is provided to measure thetemperature in the duct 12 and to supply a signal to the control means28.

The outlet 20 of the duct 12 is connected to a solid oxide fuel cellstack (not shown) via a device 34 to remove particulate carbon from thepre-reformed hydrocarbon fuel, methane. The device 34 to removeparticulate carbon is an inertial separator and in this examplecomprises a supersonic twister. The device 34 comprises a duct 36, whichhas an inlet 38 at a first end 40 and a plurality of swirl vanes 42 areprovided in the inlet 38 of the duct 36. The duct 36 also has twooutlets 44 and 46 at a second end 48. At the second end 48 of the duct36 a central duct 50 is arranged in the centre of the duct 36 and anouter duct 52 is arranged around the central duct 50. The central duct50 is connected to the outlet 44 and the outer duct 52 is connected tothe outlet 46.

The outlet 44 of the device 34 to remove particulate carbon from thepre-reformed fuel, methane, is connected to the solid oxide fuel cellstack via a reformer (not shown). The reformer may be an internalreformer or an external reformer. It is essential that the duct 12 isinert with respect to the hydrocarbon fuel to ensure that there are nochemical reactions between the duct 12 and the hydrocarbon fuel.Likewise the duct 12 must be sealed to ensure that only the hydrocarbonfuel enters the duct to ensure that the hydrocarbon fuel cannot takepart in chemical reactions.

In operation a hydrocarbon fuel, for example natural gas is supplied ata low pressure through the inlet 16 into the duct 12. The hydrocarbonfuel flows through the duct 12 and an electrical current is suppliedfrom the power supply 26 through the electrically conducting wire 14.The electrically conducting wire 14 heats the hydrocarbon fuel flowingthrough the duct 12 and causes the higher hydrocarbons in thehydrocarbon fuel to thermally decompose on the surface of theelectrically conducting wire 14. The control means 28 receives signalsfrom the temperature sensor 33 and controls the supply of the electriccurrent from the power supply 26 through the electrically conductingwire 14 to maintain the electrically conducting wire 14 at a temperatureto provide selective thermal decomposition of the higher hydrocarbonsonly in the hydrocarbon fuel.

The pre-reformed hydrocarbon fuel containing carbon particles flowsthrough the outlet 20 and exits the duct 12 and flows into the inlet 38of the device 34 to remove particulate carbon.

The pre-reformed hydrocarbon fuel and carbon particles is swirled by theswirl vanes 42 and this causes the carbon particles to be flung to theregions of the duct 36 near to the inner surface of the duct 36 and thehydrocarbon fuel remains at the centre of the duct 36. The carbonparticles then flow into the outer duct 52 at the second end 48 of thedevice 34 and through the outlet 46. The pre-reformed hydrocarbon fuelflows into the central duct 50 at the second end 48 of the device 34 andthrough the outlet 44 to the reformer and solid oxide fuel cells.

The advantages of the present invention are that coking in the solidoxide fuel cells and other parts of the solid oxide fuel cell system isreduced or prevented. The present invention operates at the inletpressure of the hydrocarbon fuel supply. The present invention is simpleand no additional reactants are required to react with the hydrocarbonfuel to remove the higher hydrocarbons. The present invention operatesindependently of the temperature and pressure constraints of the solidoxide fuel system. The present invention is located externally of thesolid oxide fuel cell system and allows ease of maintenance andreplacement.

Although the present invention has been described with reference to atwister to remove particulate carbon other suitable devices may be used,for example other inertial separators, filters or electrostaticseparators.

Although the present invention has been described with reference to asingle electrically conducting wire inside the duct it may be possible,or desirable, to use a plurality of electrically conducting wires insidethe duct. Alternatively one or more other electrically conductingmembers may be provided inside the duct, for example an electricallyconducting honeycomb etc, which would increase the surface area for heattransfer but would require more electrical power.

Although the present invention has been described with reference to anelectrically conducting wire, or electrically conducting member, insidethe duct directly connected to a power supply outside the duct, it maybe possible and advantageous to use an electrically conducting wireloop, or electrically conducting member, inside the duct indirectlyconnected to the power supply using an electrically conducting wire loopoutside the duct and using electrical inductive heating from theexternal electrical conducting wire loop to the internal electricallyconducting wire loop, or electrically conducting member.

Additionally, it may be possible for the duct, or at least a portion ofthe duct, to be an electrically conducting member and for the at least aportion of the duct to be directly, or indirectly, electrically heated.

The electrically conducting member is preferably chemically inert withrespect to the hydrocarbon fuel or may act as a catalyst to enhance thethermal decomposition of the higher hydrocarbons and/or to minimisecarbon deposition.

Although the present invention has been described with reference to asolid oxide fuel cell system, it may be applicable to other fuel cellsystems.

Although the present invention has been described with reference to usewith fuel cell systems it may be possible to use the pre-reformer with areformer for other systems.

1. A pre-reformer comprising a gas tight duct and at least oneelectrically conducting member arranged in the duct, the at least oneelectrically conducting member is electrically isolated from the duct,the duct has an inlet for receiving a hydrocarbon fuel at a first endand an outlet for supplying a pre-reformed hydrocarbon fuel at a secondend, at least the inner surface of the duct is chemically inert withrespect to the hydrocarbon fuel, an electrical power supply electricallyconnected to the at least one electrically conducting member and controlmeans to control the supply of electrical current through the at leastone electrically conducting member to maintain the at least oneelectrically conducting member at a temperature to provide selectivethermal decomposition of higher hydrocarbons in the hydrocarbon fuel. 2.A pre-reformer as claimed in claim 1 wherein the gas tight duct isnon-electrically conducting.
 3. A pre-reformer as claimed in claim 1wherein the gas tight duct comprises a ceramic, a glass-ceramic or aglass.
 4. A pre-reformer as claimed in claim 1 wherein a temperaturesensor is arranged to measure the temperature in the duct and iselectrically connected to the control means.
 5. A pre-reformer asclaimed in claim 1 wherein the at least one electrically conductingmember extends through the walls of the duct and is directlyelectrically connected to the electrical power supply.
 6. A pre-reformeras claimed in claim 5 wherein the electrically conducting member iselectrically isolated from the duct by glass seals or glass-ceramicseals.
 7. A pre-reformer as claimed in claim 1 wherein the at least oneelectrically conducting member forms a loop, a second electricallyconducting member is arranged outside the duct, the second electricallyconducting member is electrically connected to the electrical powersupply and the control means controls the supply of electrical currentthrough the second electrically conducting member to maintain the atleast one electrically conducting member at a temperature to provideselective thermal decomposition of higher hydrocarbons in thehydrocarbon fuel.
 8. A pre-reformer as claimed in claim 1 wherein the atleast one electrically conducting member comprises a honeycomb.
 9. Apre-reformer as claimed in claim 1 wherein the at least one electricallyconducting member comprises at least a portion of the duct.
 10. Apre-reformer as claimed in claim 1 wherein the at least one electricallyconducting member comprises a metal or an alloy.
 11. A pre-reformer asclaimed in claim 1 wherein the outlet of the duct is connected to a fuelcell stack.
 12. A pre-reformer as claimed in claim 11 wherein the outletof the duct is connected to a solid oxide fuel cell stack.
 13. Apre-reformer as claimed in claim 11 wherein the outlet of the duct isconnected to the fuel cell stack via means to remove particulate carbonfrom the pre-reformed hydrocarbon fuel.
 14. A pre-reformer as claimed inclaim 13 wherein the means to remove particulate carbon comprises aninertial separator.
 15. A pre-reformer as claimed in claim 14 whereinthe inertial separator comprises a twister.
 16. A pre-reformer asclaimed in claim 13 wherein the means to remove particulate carboncomprises a filter or an electrostatic separator.
 17. A pre-reformer asclaimed in claim 13 wherein the means to remove particulate carbon fromthe pre-reformed fuel is connected to the fuel cell stack via areformer.
 18. A fuel cell system comprising a pre-reformer, thepre-reformer comprising a gas tight duct and at least one electricallyconducting member arranged in the duct, the at least one electricallyconducting member is electrically isolated from the duct, the duct hasan inlet for receiving a hydrocarbon fuel at a first end and an outletfor supplying a pre-reformed hydrocarbon fuel at a second end, at leastthe inner surface of the duct is chemically inert with respect to thehydrocarbon fuel, an electrical power supply electrically connected tothe at least one electrically conducting member and control means tocontrol the supply of electrical current through the at least oneelectrically conducting member to maintain the at least one electricallyconducting member at a temperature to provide selective thermaldecomposition of higher hydrocarbons in the hydrocarbon fuel.